var obj ={
    hi:function(){
        console.log(this);
        return() =>{
            console.log(this);
        }
    },
    saiHi:function(){
        return function(){
            console.log(this);
            return() =>{
                console.log(this);
            } 
        }
    },
    say: ()=>{
        console.log(this);
    } 
}
let sayHi = obj.saiHi;
let fun1 = sayHi();
fun1();
let fun2 = sayHi.bind(obj)();
fun2();// window window